Text Gravity

using System;
using System.Collections.Generic;
using System.Security;

public class TextGravity
{
    public static void Main()
    {
        int lineLength = int.Parse(Console.ReadLine());
        string text = Console.ReadLine();

        int index = 0;

        List<char[]> matrix = new List<char[]>();

        while (index < text.Length)
        {
            char[] currentLine = new char[lineLength];

            for (int i = 0; i < lineLength; i++)
            {
                if (index < text.Length)
                {
                    currentLine[i] = text[index];
                }
                else
                {
                    currentLine[i] = ' ';
                }

                index++;
            }

            matrix.Add(currentLine);
        }

        for (int row = matrix.Count - 1; row >= 0; row--)
        {
            for (int column = 0; column < lineLength; column++)
            {
                if (matrix[row][column] != ' ')
                {
                    continue;
                }

                int currentRow = row - 1;
                while (currentRow >= 0)
                {
                    if (matrix[currentRow][column] != ' ')
                    {
                        matrix[row][column] = matrix[currentRow][column];
                        matrix[currentRow][column] = ' ';
                        break;
                    }

                    currentRow--;
                }
            }
        }

        Console.Write("<table>");

        for (int row = 0; row < matrix.Count; row++)
        {
            Console.Write("<tr>");
            for (int column = 0; column < lineLength; column++)
            {
                Console.Write("<td>{0}</td>", SecurityElement.Escape(matrix[row][column].ToString()));
            }

            Console.Write("</tr>");
        }

        Console.WriteLine("</table>");
    }
}